Of those infected, 21 have been hospitalized. No deaths have been reported. Those infected range in age from younger than 1 to 84 years old, with a median age of 18.

The cases include people who’ve eaten the beef since March 1, the agency said, but no supplier, distributor or brand of beef has been identified.

“Traceback investigations are ongoing to determine the source of raw ground beef supplied to grocery stores and restaurant locations where ill people reported eating,” the CDC said.

“Illnesses that occurred after March 29 might not yet be reported due to the time it takes between when a person becomes ill with E. coli and when the illness is reported. This takes an average of two to three weeks,” the CDC said.

Meanwhile, Grant Park Packing has recalled more than 53,000 pounds of raw ground beef products due to possible E. coli contamination, the US Department of Agriculture’s Food Safety and Inspection Service said in a statement. The Illinois company said the ground beef items were produced on October 30 and 31, and November 1.

K2D Foods/Colorado Premium Foods is also recalling more than 113,000 pounds of raw ground beef produced in late March and early April because of possible contamination.

There’s no definitive link between these products and the ongoing E. coli outbreak, the agency said.

Symptoms of E. coli infection include severe stomach cramps, diarrhea and vomiting. They begin, on average, three to four days after ingesting the bacteria. Most people recover in five to seven days.

Consumers are urged to prevent the spread of E. coli by washing hands frequently, cooking ground beef to an internal temperature of 160 degrees and keeping uncooked foods away from raw beef to prevent cross-contamination.